Device for separating dust from flue gases from combustion plants, especially solid fuel combustion plants

ABSTRACT

The invention relates to a device for separating dust from flue gases from combustion plants, especially solid fuel combustion plants, comprising at least one dust filter via which the flue gases are guided, and by means of which the dust from the flue gases can be filtered out as it passes through the dust filter. In order to produce a device which separates dust in a highly efficient manner and which can be operated in a highly reliable manner and be used to heat combustion air for the combustion plant, the at least one dust filter is embodied as a bulk material filter in whose bulk material heat from the flue gases can be collected when the bulk material is cross-flown by the flue gases and by means of whose bulk material heat collected from the flue gases when the combustion air of the combustion plant flows through the bulk material filter can be given off to said combustion air.

[0001] The invention concerns a device for separating dust from fluegases from combustion plants, especially from solid fuel combustionplants, with at least one dust filter, via which the flue gases areconducted and by means of which dust can be filtered out of the fluegases as they pass through the dust filter.

[0002] During the course of the combustion processes in combustionplants —depending on the type of fuel used—there are dust emissions,whereby, especially in the case of solid fuel combustion plants and thefuels burnt there, these are of significant importance. To prevent suchdusts being emitted into the environment, each country has differentstatutory regulations, which limit the dust content of flue gases ontheir entry into the surrounding atmosphere. Thus, for example, in theFederal Republic of Germany the 17th Ordinance for the Implementation ofthe Federal Imission Control Act (17 .BlmschV) and the TechnicalInstructions Air Quality Control 2000 (TA Luft 2000) apply, limiting thedust content of the flue gases entering into the surrounding atmosphereto <10 mg dust per standard cubic meter of flue gas.

[0003] As in the case of combustion plants used commercially, forexample, in the case of large scale boiler plants, flue gas temperaturesof over 240 degrees C. are a common occurrence, the heat contained inthe flue gases is used to prewarm the combustion air to be fed into thecombustion plant in order to better exploit the energy of the flue gasesbefore or upstream of the actual device for separating dust.

[0004] Nowadays electrostatic filter devices, for example, electrostaticfilters or fibrous filters, are used as devices for separating dust.

[0005] In known combustion plants, flue gas air preheaters (LUVO) ofvery different designs are used to preheat the combustion air, forexample, rotating air preheaters, air flow preheaters, plate preheatersetc. In addition to relatively large energy losses, these show drops inpressure and are, moreover, subject to high mechanical stresses.

[0006] The object of the invention is to develop the device describedinitially for separating dust from flue gases from combustion plants,especially solid fuel combustion plants, in such a way that with it, onthe one hand the heat contained in the flue gases of the combustionplant is more utilizable for preheating the combustion air to be fed tothe combustion plant, whereby, on the other hand, the technical designof the structure of the device for separating dust should be simplified.

[0007] This object is achieved according to the invention in that atleast one dust filter is formed as a bulk material filter, in the bulkmaterial of which heat can be taken up from the flue gases when suchflue gases flow through the bulk material filter and by means of thebulk material of such filter, when the combustion air of the combustionplant flows through the bulk material filter, the heat taken up from theflue gases can be conveyed to the combustion air.

[0008] As, in the case of the device for separating dust according tothe invention, separate flue gas air preheaters are not necessary, thereare, in comparison with the prior art, significantly less costs. Thiscan be traced back to lower pressure drops, to less consumption ofelectrical energy, to savings in maintenance and less radiation loss dueto cold surfaces. Thus the pressure drop in the case of a device forseparating dust built according to the prior art—with a flue gas flow of46500 standard cubic meters, 23.7 g water per kg air and aiming at acombustion air temperature of 128 degrees C.—is, for example, 18 mbar,as opposed to which, the pressure drop with the corresponding devicedesigned according to the invention is only 13 mbar. The suction draughtcapacity in the case of the device for separating dust according to theprior art amounts to 220 kW; in the case of the device for separatingdust according to the invention this is 150 kW. In the case of thedevice for separating dust according to the prior art, which has anelectrostatic filter as filter element, the filter current requirementis 38 kW, whereas there is no such filter current requirement in thecase of the device for separating dust according to the invention.

[0009] Expediently the device for separating gases according to theinvention has at least two bulk material filters, through which the fluegases and the combustion air can flow alternately. When the flue gasesflow through the bulk material filters the bulk material filters areheated, whereas, when the combustion air flows through the bulk materialfilters, the heat stored in the bulk material filters is released intothe combustion air.

[0010] In order to provide the bulk material filters of the device forseparating dust according to the invention with the best through flowcharacteristics, it is of advantage if each bulk material filter has amulti-surface casing, in which two grids are arranged parallel to thesurfaces, and the bulk material of the bulk material filter is heldbetween the said grids. As the two grids can have a relatively largesurface, it is possible to achieve the substantially improved throughflow characteristics aimed at in the bulk material filters used in thedevice for separating dust according to the invention.

[0011] Hereby, it is of particular advantage if the two grids each havea rectangular cross-section. Using appropriate measurements it ispossible to create a space constant with respect to its width betweenthe two grids, in which space the bulk material of the bulk materialfilter can be taken up and held.

[0012] If the bulk material of the bulk material filter or filters isformed in such a way that it has a large specific surface and a smallcontact surface, it is ensured that the conduction of heat by theindividual components of bulk materials is negligible compared to theheat uptake of the bulk material from the flue gas. This makes areversible temperature behavior curve with steep temperature gradientsin the bulk material layers possible.

[0013] Rubble capable of storing heat, especially natural chamotte, hasproven to be a particularly advantageous bulk material.

[0014] The dimensions of the grids of the bulk material filter and thethickness of the bulk material layer formed between the grids can beadvantageously arranged to match the volume of the flue gas flow and thetemperature level to be set, whereby, it goes without saying that thatalso applies to the quality of the bulk material to be chosen.

[0015] For the chronologically successive loading of the bulk materialfilter of the device for separating dust according to the invention withflue gas and combustion air, it is of advantage, if, using a flapcontrol system, either a flue gas flow or a combustion air flow can berouted through the respective bulk material filter.

[0016] In order to avoid excessive pressure drops due to high dust loadin the bulk material of the bulk material filter of the device forseparating dust according to the invention, it is recommended that inaccordance with an advantageous embodiment of the device for separatingdust according to the invention, each bulk material filter has a bulkmaterial dedusting device, by means of which the dust separated from theflue gases and taken up in the bulk material of the bulk material filtercan be separated from the bulk material.

[0017] The bulk material dedusting device of each bulk material filtercan advantageously be put into operation when the combustion air flowsthrough it relative to the pressure drop at the bulk material filter.

[0018] For removing polluted bulk materials from the space between thetwo grids of the bulk material filter, the bulk material dedustingdevice of the filter advantageously has an initial material lock placedunder the bulk material of the bulk material filter, and by means ofthis lock the bulk material dust mixture can be extracted in batchquantities from the bulk material filter. The extraction can be done bygravity because of the siting under the bulk material between the gridsof the bulk material filter.

[0019] Expediently, the bulk material dedusting device of each bulkmaterial filter has a lower collecting tank placed in the material flowdirection downstream of the first material lock, from which tank thebulk material dust mixture can be routed to a cyclone separator using aconveying airflow, whereby the bulk material and the dust can beseparated from each other.

[0020] The bulk material with the dust removed goes from a bulk materialremoval outlet of the cyclone separator into an upper collecting tank,from which it is returned between the grids of the bulk material filterby means of a second material lock. The collecting tank or the secondmaterial lock is arranged above the two grids, so that the introductionof the cleaned bulk material into the space between the two grids canalso be effected by gravity.

[0021] It is of advantage if a dust exhaust or an outgoing airflow fromthe cyclone separator of the bulk material dedusting device of each bulkmaterial filter leads to an ash collecting tank or to a fibrous filter.

[0022] In a method according to the invention for separating dust fromflue gases from combustion plants, especially solid fuel combustionplants, in which method the flue gases are dedusted in dust filters, theheat contained in the flue gases is stored in the bulk material of thedust filter constructed as a bulk material filter and the heat stored inthe bulk material is released to the combustion air flowing through thebulk material filter.

[0023] With the method according to the invention, it is possible toattain heat recovery levels of over 95%. According to a particularlyadvantageous development of the method according to the invention, eachbulk material filter is switched from the flue gas flow into thecombustion airflow, as soon as or shortly before the bulk materialfilter reaches the flue gas temperature at its outlet side. Hereby themaximum heat uptake capacity of the bulk material is exploited, wherebythis maximum heat taken up is then also available to cool the combustionair.

[0024] Expediently, the bulk material is cleaned of the dust taken up byit while the bulk material filter emits heat to the combustion aircurrent, whereby the cleaning process can be carried out continuously.

[0025] Of advantage is that the polluted bulk material is removed fromthe bulk material filter in batch quantities by gravity, whereby thedust and the bulk material are separated from each other, before thecleaned bulk material is returned to the bulk material filter in batchquantities by gravity.

[0026] In the following, the invention is explained in greater detailusing an embodiment and with reference to the drawings.

[0027] The following is depicted:

[0028]FIG. 1 an embodiment of a device according to the invention forseparating dust from flue gases from combustion plants, especially fromsolid fuel combustion plants;

[0029]FIG. 2 a basic illustration for the invention of essentialcomponents of a dust or bulk material filter of the device, according tothe invention, for separating dust shown in FIG. 1; and

[0030]FIG. 3 a basic illustration of flue gases, which flow through abulk material filter of the device for separating dust shown in FIG. 1.

[0031] An embodiment of a device 1, according to the invention, forseparating dust from flue gases from combustion plants, especially solidfuel combustion plants, is shown in a basic illustration in perspectivein FIG. 1 and serves to reduce the dust content of flue gases that occurin the combustion plant during the combustion process. Thus, in theFederal Republic of Germany, for example, currently such flue gases musthave a dust content of only <10 mg per standard cubic meter when theyenter the surrounding atmosphere (17 . BlmschV and TA Luft 2000).

[0032] Using a suction draught device 3, a flue gas flow 2, shown inFIG. 1, and removed from the combustion plant is routed through thedevice 1 for separating dust shown in FIG. 1. In the opposite direction,using a fresh air fan 4, combustion airflow 5 is led through the device1 for separating dust and from there to the combustion plant.

[0033] In the embodiment shown in FIG. 1, the device 1 for separatingdust shown there has two dust filters 6, 7. The dust filters 6, 7 are,as will be described later, each constructed as bulk material filters 6,7.

[0034] Flue gas flow 2 and combustion airflow 5 flow alternately througheach dust or bulk material filter 6, 7. To that purpose, in the linesystem of the device 1 for separating dust in the embodimentrepresented, eight valves 8, 9, 10, 11, 12, 13, 14 and 15 are providedfor, which form a flap control system 8 to 15 for the two dust or bulkmaterial filters 6, 7.

[0035] When flue gas flow 2 flows through the upper dust or bulkmaterial filter 6 in FIG. 1 and combustion airflow 5 flows through thelower dust or bulk material filter 7 in FIG. 1, the valve 8 is closed,the valve 9 open, the valve 10 closed, the valve 11 open, the valve 12open, the valve 13 closed, the valve 14 closed and the valve 15 open.The flue gas flow 2 is routed through the valve 9 into the upper dust orbulk material filter 6 in FIG. 1 and from there through the valve 12 tothe suction draught device 3; accordingly, the combustion airflow 5 isrouted by the fresh air fan 4 through the valve 15, the lower dust orbulk material filter 7 in FIG. 1 and the valve 11 on to the combustionplant.

[0036] When the flue gas flow 2 is routed through lower dust or bulkmaterial filter 7 in FIG. 1 and the combustion airflow 5 through theupper dust or bulk material filter 6 in FIG. 1, then valve 8 is open,the valve 9 closed, the valve 10 open, the valve 11 closed, the valve 12closed, the valve 13 open, the valve 14 open and the valve 15 closed.The flue gas flow 2 is routed through the valve 10 to the lower dust orbulk material filter 6 in FIG. 1 and from there to the suction draughtdevice 3 via the valve 14; accordingly, the combustion airflow 5 isrouted through the valve 13 to the upper dust or bulk material filter 6in FIG. 1 and from there through the valve 8 to the end section facingthe combustion plant of the device 1 for separating dust.

[0037] As already mentioned, the flue gas flow 2 and combustion airflow5 alternately flow through the two dust or bulk material filters 6, 7.

[0038] As can be seen from FIGS. 2 and 3, each dust or bulk materialfilter 6, 7 is constructed as follows:

[0039] Each dust or bulk material filter 6, 7 has a multi-surface casing16, in the interior of which two grids 17, 18 are arranged with theirsurfaces parallel to each other. As can be seen from FIG. 3, thedimensions of the inner grid 18 are slightly less than those of theouter grid 17, thus forming a space or reception area for bulk material19 between the two grids 17, 18. The entire space between the grids 17,18 is filled up with bulk material 19. The bulk material 19 ispreferably rubble capable of storing heat, e.g. natural chamotte.

[0040] As is shown particularly in FIG. 3, the hot flue gases 20entering the device 1 for separating dust from the combustion plant areintroduced into the interior of the dust or bulk material filter 6, 7formed by the two grids 17, 18 and the bulk material 19. In order toleave the dust or bulk material filter 6, 7, the hot flue gases 20 haveto flow through the bulk material 19 which is held between the grids 17,18. Hereby, the dust contained in the flue gases 20 is separated veryeffectively from the flue gases 20. Moreover, when the flue gases 20pass through the bulk material 19, heat contained in the flue gases 20is taken up by the bulk material 19 and stored.

[0041] The rubble capable of storing heat chosen as the bulk material 19contains, in comparison with its specific surface, only very few contactsurfaces. Thus heat transfer takes place almost exclusively between theflue gases 20 and the bulk material 19, whereas the transfer of heat orconduction of heat within the bulk material 19 is negligible.Correspondingly, a reversible temperature behavior curve with steeptemperature gradients appears in the layering which contains the bulkmaterial 19.

[0042] As soon as a temperature breakthrough through the layering of thebulk material 19 is imminent, i.e. as soon as the temperature in thearea of the outlet side 21 or the outer grating 17 reaches flue gastemperature, the supply of flue gases 20 to the respective dust or bulkmaterial filter 6, 7 is interrupted, whereby the flue gases 20 are sentto the respective other dust or bulk material filter 7 or 6, as has beendescribed using FIG. 1.

[0043] The combustion airflow 5 then flows through the dust or bulkmaterial filter 6, 7 heated to the flue gas temperature by the fluegases 20. Hereby, the combustion airflow 5 is heated and the dust orbulk material filter 6 is recooled.

[0044] In the design of the dust or bulk material filter 6, 7, the sizesof the grids 17, 18 as well the layer thickness of the bulk material 19is adapted to the flue gas mass flow 2 expected in the operation of thedevice 1 for separating dust and to the flue gas temperature expected aswell as the desired temperature of the combustion air.

[0045] As the flue gas flow 2 flows through the dust or bulk materialfilter 6, about 99% of the dusts contained in the flue gas flow 2 or inthe flue gases 20 are separated. As the combustion airflow 5 flowsthrough the dust or bulk material filter 6, 7 after the latter has beenwarmed up by the flue gases 20, over 95% of the heat stored in the bulkmaterial 19 of the dust or bulk material filter 6, 7 can be released tothe combustion airflow 5. That means that with the dust or bulk materialfilter 6, 7 described above, heat recovery levels of >95% are possible.In the dimensioning of the dust or bulk material filter 6, 7 of thedevice 1 for separating dust, consideration will also be given to othereconomic aspects and to the intended change-over cycles with respect tothe loading with flue gas or combustion air.

[0046] As can be seen especially in FIG. 2, each dust or bulk materialfilter 6, 7 is equipped with a bulk material dedusting device 22.

[0047] This is described in more detail below.

[0048] When the combustion airflow 5 flows through the dust or bulkmaterial filter 6, 7,—controlled by the pressure drop at the dust orbulk material filter 6, 7— the bulk material 17 is dedusted. The bulkmaterial 19 is held between the inner, smaller grating 18 and the outer,larger grating 17. In the lower area of the dust or bulk material filter6, a first material lock 23, represented only in principle in FIG. 2, isprovided. Through this first material lock 23, the mixture from bulkmaterial 19, and the dust taken up in it, is extracted in batchquantities by gravity out of the space between the grids 17, 18. Hereby,the said mixture of dust and bulk material 19 arrives in a lowercollecting tank 24, from which the mixture is routed to a dedustingcyclone or cyclone separator 26 by means of a pressure or conveyingairflow 25. In the dedusting cyclone or cyclone separator 26, the dustand the bulk material 19 are separated from each other, whereby the bulkmaterial 19 with the dust removed is blown via a bulk material removaloutlet 27 of the dedusting cyclone or cyclone separator 26 into acollecting tank (not shown in FIG. 2) placed above the space between thegrids 17, 18. The cleaned bulk material is reintroduced by gravity intothe space between the two grids 17, 18 of the dust or bulk materialfilter 6 through a second material lock 28 which is also represented inprinciple only.

[0049] The outgoing air (precleaned up to 95%) from the dedustingcyclone or cyclone separator 26 undergoes afterpurification via afibrous filter; a dust exhaust 29 of the dedusting cyclone or cycloneseparator 26 is routed to an ash collecting tank.

[0050] The dust or bulk material filters 6, 7 of the device 1 forseparating dust according to the invention and described in greaterdetail using the Figures above, also act as a preheating filter or asintegrated air preheating for the combustion airflow 5 to the combustionplant. Thus it is possible to do without other measures for preheatingthe air of the combustion airflow 5, or such measures can be reduced.

1. Device for separating dust from flue gases from combustion plants,especially solid fuel combustion plants, with at least one dust filter(6, 7), via which the flue gases (20) are routed and by means of whichdust can be filtered out from the flue gases (20) as they pass throughthe filter (6, 7), wherein the dust filter (6, 7), of which there is atleast one, is formed as a bulk material filter (6, 7), in the bulkmaterial (19) of which, when the flue gases (20) flow through the bulkmaterial filter (6, 7), the heat from the flue gases (20) can be takenup and by means of the bulk material (19) of the said filter, whencombustion air (5) from the combustion plant flows through the bulkmaterial filter (6, 7), the heat taken up from the flue gases (20) canbe released to this combustion air (5).
 2. Device for separating dustaccording to claim 1, that has at least two bulk material filters (6,7), through which the flue gases (20) and the combustion air (5) canflow alternately.
 3. Device for separating dust according to claim 1 or2, in which each bulk material filter (6, 7) has a multi-surface casing(16), in which two grids (17, 18) are arranged with their surfacesparallel to each other, between which grids the bulk material (19) ofthe bulk material filter (6, 7) is held.
 4. Device for separating dustaccording to claim 3, in which the two grids (17, 18) each have arectangular cross-section.
 5. Device for separating dust according toone of the claims 1 to 4, in which the bulk material (19) of the bulkmaterial filter or filters (6, 7) is formed in such a way that it has alarge specific surface and a small contact surface.
 6. Device forseparating dust according to one of the claims 1 to 5, in which the bulkmaterial (19) of the bulk material filter or filters (6, 7) is formed asrubble capable of storing heat, preferably as natural chamotte. 7.Device for separating dust according to one of the claims 3 to 6, inwhich the dimensions of the grids (17, 18) of the bulk material filter(6, 7) and the thickness of the bulk material layer formed between thegrids (17, 18) can be realized to match the volume of the flue gas flowand the temperature level to be set.
 8. Device for separating dustaccording to one of the claims 1 to 7, in which the flue gas flow (2)and the combustion airflow (5) can be routed through each bulk materialfilter (6, 7) in chronological sequence by means of a flap controlsystem (8 to 15).
 9. Device for separating dust according to one of theclaims 1 to 8, in which each bulk material filter (6, 7) has a bulkmaterial dedusting device (22), by means of which device the dustseparated from the flue gases (20) and taken up in the bulk material(19) of the bulk material filter (6, 7) can be separated from the bulkmaterial (19).
 10. Device for separating dust according to claim 9, inwhich the bulk material dedusting device (22) of the bulk materialfilter (6, 7), when the combustion air (5) is flowing through the saidfilter, can be put into operation as a function of the pressure drop atthe bulk material filter (6, 7).
 11. Device for separating dustaccording to claim 9 or 10, in which the bulk material dedusting device(22) of each bulk material filter (6, 7) has a first material lock (23)placed under the bulk material (19) of the bulk material filter (6, 7),by means of which bulk material dust mixture can be extracted from thebulk material filter (6, 7) in batch quantities.
 12. Device forseparating dust according to claim 11, in which the bulk materialdedusting device (22) of each bulk material filter (6, 7) has a lowercollecting tank (24) arranged in the material flow direction downstreamof the first material lock (23), from which tank the bulk material dustmixture can be routed by means of a conveying airflow (25) to a cycloneseparator (26), in which the bulk material (19) and the dust can beseparated from each other.
 13. Device for separating dust according toclaim 12, in which the bulk material dedusting device (22) of eachmaterial filter (6, 7) has an upper collecting tank arranged in materialflow direction downstream of a bulk material removal outlet (27) of thecyclone separator (26) and above the bulk material (19) of the bulkmaterial filter (6, 7), from which tank the cleaned bulk material (19)can be returned by means of a second material lock (28) between thegrids (17, 18) of the bulk material filter (6, 7).
 14. Device forseparating dust according to claim 12 or 13, in which a dust exhaust(29) or an outgoing airflow of the cyclone separator (26) of the bulkmaterial dedusting device (22) of each bulk material filter (6, 7) isrouted to an ash collecting tank or to a fibrous filter.
 15. Method forseparating dust from flue gases from combustion plants, especially solidfuel combustion plants, in which the flue gases (20) are dedusted indust filters (6, 7), wherein heat contained in the flue gases (20) isstored in the bulk material (19) of the dust filter (6, 7) formed as abulk material filter (6, 7), and the heat stored in the bulk material(19) is released to the combustion air (5) flowing through the bulkmaterial filter (6, 7).
 16. Method for separating dust according toclaim 15, in which each bulk material filter (6, 7) is switched from theflue gas flow (2) into the combustion airflow (5), as soon as, orshortly before the bulk material filter (6, 7) reaches the flue gastemperature at its outlet side (21).
 17. Method for separating dustaccording to claim 15 or 16, in which the bulk material (19) is cleanedof the dust it absorbed while the bulk material filter (6, 7) transfersheat to the combustion airflow (5).
 18. Method for separating dustaccording to claim 17, in which the polluted bulk material (19) isremoved from the bulk material filter (6, 7) in batch quantities bygravity, the dust and the bulk material (19) are separated from eachother and the cleaned bulk material (19) is routed by gravitation to thebulk material filter (6, 7) in batch quantities.